1. Field of the Invention
The present invention relates to a magnetic head in which a magnetic metal film comprising a Co-containing amorphous alloy and a crystallizable glass of the PbO-B.sub.2 O.sub.3 -ZnO system as a solder glass are used.
2. Description of the Prior Art
In recent years, floppy disk devices and hard disk devices used as an external memory of various computers have been advanced whereby such devices have become small and have obtained a high recording density. Therefore, a magnetic head, which can be viewed as the heart of the disk device, is also required to have a high performance, and hence a magnetic head has been developed in which a magnetic amorphous metal film (Co-Nb-Zr alloy) having a saturated magnetic density of high volume is used.
These magnetic heads are mainly formed with a head core, which is made of a magnetic material, and a ceramic slider, which is made of a non-magnetic material, by a joining technique with glass.
The joining process contains two steps which comprise a step wherein, after filling of glass to a magnetic head core, gaps of the head cores are joined to each other by glass, and a step wherein a head chip cut off from the head core are joined to a ceramic slider by glass.
In this case, the magnetic core is filled with glass at a temperature of about 420.degree. C. (but 420.degree. C. or below) and once the temperature is lowered naturally. Thereafter, the gaps of the head cores are joined to each other by glass at a temperature of 450.degree. C. Furthermore, the head chip cut off from the head core is joined to the ceramic slider at a temperature of from exceeding 450.degree. C. up to 460.degree. C. by glass.
In this case, the magnetic amorphous metal film is crystallized when heated to the temperature of higher than 500.degree. C., resulting in extreme deterioration of magnetic properties. Therefore, it is important to select the glass which is workable at a temperature of 500.degree. C. or less and has a thermal expansion coefficient as near as possible to those of the head core and the ceramic slider in order that the magnetic head may not crack due to the difference of the thermal expansion caused by the temperature change in the construction procedures.
When an amorphous glass is used as the solder glass (abbreviated as glass A) for joining the gaps of the head cores, it is necessary to select a solder glass (abbreviated as glass B) for joining the head chip to the ceramic slider such that a glass B enables joining at a temperature lower than the softening temperature of glass A so that size distortion may not occur.
Thus, the softening temperatures of glass A and glass B must differ greatly. Moreover, a glass having a low softening temperature has a large thermal expansion coefficient and hence, the selection of glass is not easy.
On the other hand, though an adhesive such as an epoxy resin or the like is effective because it is workable at 300.degree. C. or below and hence the magnetic amorphous metal film is not influenced, it is difficult to maintain very precise gaps thereby.
Under these circumstances, use of a crystallizable glass has been investigated as the glass A, and the glass is improved in thermal resistance by crystallization, whereby the working temperature of the glass B is elevated. That is, it is desired that the glass A has an elevated melting temperature when it is crystallized.
Thus, even if the working temperature of glass B is raised to the working temperature of glass A, the glass A which has been crystallized once is not melted at the initial working temperature, so that the glass A itself can be used as the glass B.
Further, an amorphous glass may of course be used as the glass B. In this case, it is preferable to select and use those fit for the thermal expansion coefficient of the glass A.
The joining of gaps of the head cores comprises bringing two cores in which their head core grooves have been filled with glass face to face and heating them to join them.
In the glass filling operation, it is impossible to join the cores when the glass is crystallized. Therefore, it is necessary to select as the glass A a crystallizable glass having characteristics such that it is not crystallized during the above-mentioned glass filling while it is crystallized at the core joining time.
Japanese Patent Application Kokai (Laid-Open) No. 20265/1980 discloses a sealing glass consisting of:
______________________________________ PbO 77.about.86 wt % ZnO 7.about.12 wt % B.sub.2 O.sub.3 7.about.11 wt % SiO.sub.2 1.about.3 wt % ______________________________________
However, this glass composition is crystallized during the above-mentioned filling operation. Due to the crystallization, it is necessary to raise the working temperature for joining in the subsequent joining step higher than normally required. This is not preferable for joining the gaps of the magnetic head.